* [PATCH] blk-cgroup: Use cond_resched() when destroy blkgs
@ 2021-01-26 13:33 Baolin Wang
2021-01-27 14:37 ` Tejun Heo
0 siblings, 1 reply; 4+ messages in thread
From: Baolin Wang @ 2021-01-26 13:33 UTC (permalink / raw)
To: axboe, tj; +Cc: joseph.qi, baolin.wang, linux-block, cgroups, linux-kernel
On !PREEMPT kernel, we can get below softlockup when doing stress
testing with creating and destroying block cgroup repeatly. The
reason is it may take a long time to acquire the queue's lock in
the loop of blkcg_destroy_blkgs(), thus we can use cond_resched()
instead of cpu_relax() to avoid this issue, since the
blkcg_destroy_blkgs() is not called from atomic contexts.
[ 4757.010308] watchdog: BUG: soft lockup - CPU#11 stuck for 94s!
[ 4757.010698] Call trace:
[ 4757.010700] blkcg_destroy_blkgs+0x68/0x150
[ 4757.010701] cgwb_release_workfn+0x104/0x158
[ 4757.010702] process_one_work+0x1bc/0x3f0
[ 4757.010704] worker_thread+0x164/0x468
[ 4757.010705] kthread+0x108/0x138
Signed-off-by: Baolin Wang <baolin.wang@linux.alibaba.com>
---
block/blk-cgroup.c | 2 +-
1 file changed, 1 insertion(+), 1 deletion(-)
diff --git a/block/blk-cgroup.c b/block/blk-cgroup.c
index 3465d6e..af7c0ce 100644
--- a/block/blk-cgroup.c
+++ b/block/blk-cgroup.c
@@ -1028,7 +1028,7 @@ void blkcg_destroy_blkgs(struct blkcg *blkcg)
spin_unlock(&q->queue_lock);
} else {
spin_unlock_irq(&blkcg->lock);
- cpu_relax();
+ cond_resched();
spin_lock_irq(&blkcg->lock);
}
}
--
1.8.3.1
^ permalink raw reply related [flat|nested] 4+ messages in thread
* Re: [PATCH] blk-cgroup: Use cond_resched() when destroy blkgs
2021-01-26 13:33 [PATCH] blk-cgroup: Use cond_resched() when destroy blkgs Baolin Wang
@ 2021-01-27 14:37 ` Tejun Heo
2021-01-28 1:35 ` Baolin Wang
0 siblings, 1 reply; 4+ messages in thread
From: Tejun Heo @ 2021-01-27 14:37 UTC (permalink / raw)
To: Baolin Wang; +Cc: axboe, joseph.qi, linux-block, cgroups, linux-kernel
Hello, Baolin.
On Tue, Jan 26, 2021 at 09:33:25PM +0800, Baolin Wang wrote:
> On !PREEMPT kernel, we can get below softlockup when doing stress
> testing with creating and destroying block cgroup repeatly. The
> reason is it may take a long time to acquire the queue's lock in
> the loop of blkcg_destroy_blkgs(), thus we can use cond_resched()
> instead of cpu_relax() to avoid this issue, since the
> blkcg_destroy_blkgs() is not called from atomic contexts.
>
> [ 4757.010308] watchdog: BUG: soft lockup - CPU#11 stuck for 94s!
> [ 4757.010698] Call trace:
> [ 4757.010700] blkcg_destroy_blkgs+0x68/0x150
> [ 4757.010701] cgwb_release_workfn+0x104/0x158
> [ 4757.010702] process_one_work+0x1bc/0x3f0
> [ 4757.010704] worker_thread+0x164/0x468
> [ 4757.010705] kthread+0x108/0x138
>
> Signed-off-by: Baolin Wang <baolin.wang@linux.alibaba.com>
* Can you please add might_sleep() at the top of the function?
* Given that the system can accumulate a huge number of blkgs in
pathological cases, I wonder whether a better way to go about it is
explicitly testing need_resched() on each loop and release locks and do
cond_resched() if true?
Thanks.
--
tejun
^ permalink raw reply [flat|nested] 4+ messages in thread
* Re: [PATCH] blk-cgroup: Use cond_resched() when destroy blkgs
@ 2021-01-28 1:35 ` Baolin Wang
0 siblings, 0 replies; 4+ messages in thread
From: Baolin Wang @ 2021-01-28 1:35 UTC (permalink / raw)
To: Tejun Heo; +Cc: axboe, joseph.qi, linux-block, cgroups, linux-kernel
Hi Tejun,
> Hello, Baolin.
>
> On Tue, Jan 26, 2021 at 09:33:25PM +0800, Baolin Wang wrote:
>> On !PREEMPT kernel, we can get below softlockup when doing stress
>> testing with creating and destroying block cgroup repeatly. The
>> reason is it may take a long time to acquire the queue's lock in
>> the loop of blkcg_destroy_blkgs(), thus we can use cond_resched()
>> instead of cpu_relax() to avoid this issue, since the
>> blkcg_destroy_blkgs() is not called from atomic contexts.
>>
>> [ 4757.010308] watchdog: BUG: soft lockup - CPU#11 stuck for 94s!
>> [ 4757.010698] Call trace:
>> [ 4757.010700] blkcg_destroy_blkgs+0x68/0x150
>> [ 4757.010701] cgwb_release_workfn+0x104/0x158
>> [ 4757.010702] process_one_work+0x1bc/0x3f0
>> [ 4757.010704] worker_thread+0x164/0x468
>> [ 4757.010705] kthread+0x108/0x138
>>
>> Signed-off-by: Baolin Wang <baolin.wang@linux.alibaba.com>
>
> * Can you please add might_sleep() at the top of the function?
Sure.
>
> * Given that the system can accumulate a huge number of blkgs in
> pathological cases, I wonder whether a better way to go about it is
> explicitly testing need_resched() on each loop and release locks and do
> cond_resched() if true?
Yes, sound better to to me and will update in next version. Thanks for
your sugestion.
^ permalink raw reply [flat|nested] 4+ messages in thread
* Re: [PATCH] blk-cgroup: Use cond_resched() when destroy blkgs
@ 2021-01-28 1:35 ` Baolin Wang
0 siblings, 0 replies; 4+ messages in thread
From: Baolin Wang @ 2021-01-28 1:35 UTC (permalink / raw)
To: Tejun Heo
Cc: axboe-tSWWG44O7X1aa/9Udqfwiw,
joseph.qi-KPsoFbNs7GizrGE5bRqYAgC/G2K4zDHf,
linux-block-u79uwXL29TY76Z2rM5mHXA,
cgroups-u79uwXL29TY76Z2rM5mHXA,
linux-kernel-u79uwXL29TY76Z2rM5mHXA
Hi Tejun,
> Hello, Baolin.
>
> On Tue, Jan 26, 2021 at 09:33:25PM +0800, Baolin Wang wrote:
>> On !PREEMPT kernel, we can get below softlockup when doing stress
>> testing with creating and destroying block cgroup repeatly. The
>> reason is it may take a long time to acquire the queue's lock in
>> the loop of blkcg_destroy_blkgs(), thus we can use cond_resched()
>> instead of cpu_relax() to avoid this issue, since the
>> blkcg_destroy_blkgs() is not called from atomic contexts.
>>
>> [ 4757.010308] watchdog: BUG: soft lockup - CPU#11 stuck for 94s!
>> [ 4757.010698] Call trace:
>> [ 4757.010700] blkcg_destroy_blkgs+0x68/0x150
>> [ 4757.010701] cgwb_release_workfn+0x104/0x158
>> [ 4757.010702] process_one_work+0x1bc/0x3f0
>> [ 4757.010704] worker_thread+0x164/0x468
>> [ 4757.010705] kthread+0x108/0x138
>>
>> Signed-off-by: Baolin Wang <baolin.wang-KPsoFbNs7GizrGE5bRqYAgC/G2K4zDHf@public.gmane.org>
>
> * Can you please add might_sleep() at the top of the function?
Sure.
>
> * Given that the system can accumulate a huge number of blkgs in
> pathological cases, I wonder whether a better way to go about it is
> explicitly testing need_resched() on each loop and release locks and do
> cond_resched() if true?
Yes, sound better to to me and will update in next version. Thanks for
your sugestion.
^ permalink raw reply [flat|nested] 4+ messages in thread
end of thread, other threads:[~2021-01-28 1:36 UTC | newest]
Thread overview: 4+ messages (download: mbox.gz / follow: Atom feed)
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2021-01-26 13:33 [PATCH] blk-cgroup: Use cond_resched() when destroy blkgs Baolin Wang
2021-01-27 14:37 ` Tejun Heo
2021-01-28 1:35 ` Baolin Wang
2021-01-28 1:35 ` Baolin Wang
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